In computer networking, a port is a physical communication endpoint where information is sent and received. At the software or operating system level, it is a logical concept that identifies a specific network service.

Ports are like openings or entry points such as doors that allow access into a house, and services are like the traffic that uses those entry points into the house. Certain services are by default required to use certain entry points (ports) on a computer.

When a service listens on a port, it can receive data from a client application, process it, and communicate a response. For example, the standard port for the Simple Mail Transfer Protocol (SMTP) traffic is 25, 465, and 587. So, if we find these ports open, we can be pretty sure that SMTP service is running or can be run on that machine.

Here is our list of the Best Online Port Scanners:

  • NMap Port Scanner EDITOR’S CHOICE This website implements the well-known Nmap tool from its Web location and offers free and paid accounts. Paid uswers can run scans continuously and probe their network devices as well as internet-facing gateways.
  • DNS Tools A popular free online service that offers a collection of network analysis tools such as port scanners, DNS Query, Traceroute, Ping, among others.
  • WhatIsMyIp A popular online service that provides a free and commercial port scanning tool.
  • Port Checker Α simple and free online tool for checking open ports on your device.
  • DNS Checker Α website that hosts a collection of tools such as DNS check tools, email tools, IP tools, developer tools, network tools–which also includes a port scanner.
  • IPVoid Α free service developed by the NoVirusThanks project whose mission it says is to “provide useful tools to troubleshoot network problems and to help in gathering information about IP addresses”
  • Hidemy Αn organization that deals primarily on VPN but it also hosts a collection of online tools and services such as proxy checker, anonymity checker, email checker, port scanner.

Why should I scan the ports on my network?

Port scanning is the method used for identifying what ports are open on a target system or network, and the services running on them. It is one of the most popular techniques used by attackers to identify “open doors” on a computer and learn about services that they can exploit in order to gain unauthorized access to the system or network. Once privileged access is obtained, the intruder can carry out malicious acts. For example, SSH normally uses port 22. So if an attacker finds that port open and listening, he knows that SSH is probably enabled on the machine. He can then try to penetrate the system by attempting to bypass or crack the login password.

This is why network administrators and security managers need to carry out regular port scans on their systems and networks to discover and mitigate possible security vulnerabilities associated with the open ports. Knowing which network services are exposed to the outside world is essential for securing the network perimeter. Having more ports open than necessary is considered a security risk, and should be urgently addressed. Port scanning will help you answer key questions such as, what ports are open? And what services and their versions are running on the open ports? You can then use the information to determine if the open ports meet with your organization’s security policy.

Why use an online port scanner?

There are lots of port scanning applications out there that you can use to scan your network. Some have to be locally installed on the target machine, while others are delivered online.

In this article, we’re going to review the eight best online port scanning applications out there.  Hopefully, this will guide you in the process of selecting the right one for your port scanning needs.

The Best Online Port Scanners

1. NMap Port Scanner

Our methodology for selecting online port scanners

We reviewed the market for websites that offer port scanning and analyzed the options based on the following criteria:

  • A reliable website that isn’t a hacker scam
  • A system that will test internet-facing ports on company routers
  • The option to set up an account and run continuous scanning
  • A service that includes availability testing
  • An easy-to-read report that identifies open ports
  • A free service or a paid tool that offers a free version for assessment
  • An online port scanner that provides value for money either because it is free or because it offers extra services that free tools don’t provide

NMap port scanner is a well-known free and open-source online tool for finding open TCP ports and running services (including their versions). The scanner allows you to easily map your network perimeter, check firewall rules and verify if your services are reachable from the Internet. NMap port scanner is part of a collection of scan services known as NMap Online.

This website’s mechanisms are based on the well-known Nmap service, as are many of similar online port scanners.

Key Features:

  • Easy to access
  • Quick external scan
  • Scheduled option
  • Recursive test in paid account
  • Internal network scan with paid account

In order to determine if a TCP port is open, Nmap sends packets to the target device and analyzes the responses. It does this by taking advantage of the three-way TCP handshake mechanism—SYN, SYN-ACK, and ACK. Once open ports are found, it goes further to determine the exact type of service (including its version) running on that port.

Nmap evolved from a simple port scanner to a robust tool containing advanced fingerprinting capabilities and a complex scripting engine. It now provides a number of features for probing computer networks, including host discovery and OS fingerprinting. These features are extensible by scripts that provide more advanced service detection, vulnerability detection, and other features.

Pros:

  • Provides a port scan of any internet-facing device
  • Publishes scan results on the website
  • Scans for paid accounts can be kept private
  • Section explaining the original Nmpa command
  • Scan well-known ports or all ports

Cons:

  • Not affiliated with the owners of the Nmap security scanner

2. DNS Tools

EDITOR’S CHOICE

The Nmap Port Scanner from Nmap Online is our top pick for an online port scanner because it offers a quick scan that anyone can get immediately by entering an address in the website, it also enables you to set up an account to store results, and it is also available as a paid service with more sophisticated features. The online port scanner provides external scanning and publishes the results. You don’t need to own the network that the scan targets. You need to get a paid account to keep your scan results private and use options such as internal port scanning.

OS: Web based

DNS Tools is a popular free online service that offers a collection of network analysis tools such as port scanners, DNS Query, Traceroute, Ping, among others.

  • Easy-to-read results
  • Scans the most important ports
  • Other connection tests available
  • On-demand scans

DNS Tools can help you answer the questions such as:

  • What’s the IP address I am connected to on the Internet?
  • Is my computer reachable from the outside through open ports?
  • Over which nodes does the connection travel?
  • How is the response time of the server?

With DNS Tools port scanner, you can determine which ports or services running on your network or device are reachable outside of your local network. You can do this for multiple ports or single ports. A single port can be verified by using the following format: 208.80.152.2:4444 (the port is separated from the IP address by a colon).

  • Completely free service

  • Simple to use – great for quick scans and non-technical users

  • Offers testing through a GUI

  • Includes a collection of testing tools

  • Advanced users might want more testing features

  • Cannot test on devices that are offline

3. WhatIsMyIp

WhatIsMyIp is a popular online service that provides a free and commercial port scanning tool.

  • Free option
  • On-demand scans
  • Scan one or many ports

It also provides other tools (free and commercial) that allow users to perform network lookups such as IP address lookup, DNS lookup, Whois lookup, and more.

WhatIsMyIp port scanner scans your network for open ports. If a port is displayed as open, that means it is open for remote communication and needs to be closed. To use this tool, go to the port scanning section of the site and enter a valid IP address at the top of the page as shown in Figure 3.0. Then select your preferred port scan option and enter the port number(s) as the case may be to begin. Details of the various port scan options are as shown in Table 1.0 below:

  • Offers both a free and commercial version

  • Great for remote troubleshooting to assist end users

  • Simple interface – straightforward troubleshooting solutions

  • Includes a collection of tools such as traceroute and reverse lookups

  • Advanced users might want more testing features

4. Port Checker

Port Checker is a simple and free online tool for checking open ports on your device.

  • Single port check
  • On-demand
  • No account required

It is a useful tool for testing port forwarding settings on a router, for diagnosing issues with blocked application ports by your firewall or ISP, and for many other security purposes.

Furthermore, if you host and play online games, this online port scanner could be used to ensure that the relevant server port is configured properly for port forwarding so that only allowed participants would be able to connect to your server.

  • As simple as it gets

  • Completely free

  • Ideal for quick checks and very basic troubleshooting

  • Lacks advanced scanning capabilities

5. DNS Checker

DNS Checker is a website that hosts a collection of tools such as DNS check tools, email tools, IP tools, developer tools, network tools–which also includes a port scanner, among others.

  • Scan multiple ports
  • On-demand scans
  • Other network tests available

The DNS Checker port scanner checks the most common ports used by Windows services, Ubuntu servers, online games, or other software. With its pre-defined list of all available used ports, you can easily use this tool to check which ports are open on your network or device by simply entering your IP address or domain name. It also allows you to define custom ports for checking if they are open for external requests, so as to prevent any external attacks on your IP.

  • Includes a host of tools

  • Check most common ports verse all possible ports

  • Ideal for quick tests

  • Not ideal for long-term testing

6. IPVoid

IPVoid is a free service developed by the NoVirusThanks project whose mission it says is to “provide useful tools to troubleshoot network problems and to help in gathering information about IP addresses”.

  • Scan a single port
  • Scan well-known ports
  • Uses Nmap

It started out as an IP blacklist checker service but later expanded its services to include more IP and network tools to make it more valuable to Internet users, researchers, and system administrators.

The IPVoid port scanner is a TCP port scanner powered by Nmap. With this tool, you can scan an IP address for open ports, check what services are running on your server such as apache, mail, ssh, FTP, MySQL, telnet, DNS, test if your firewall is working correctly, and view open TCP ports.  All it takes is to enter your IP address and choose either to scan all common ports or a custom port.

  • Essentially a GUI version of Nmap

  • Includes IP blacklist checking

  • Ideal for the beginning of troubleshooting tasks

  • Better suited for administrators

7. Hidemy Port Scanner

Hidemy is an organization that deals primarily on VPN. But it also hosts a collection of online tools and services such as proxy checker, anonymity checker, email checker, port scanner, and a host of others.

  • Enter a domain name or IP address
  • Scans performed with Nmap
  • On-demand

Hidemy port scanner is also powered by NMap and can be used to discover ports that are open on your computer or server, and what services they are running and are responsible for. To check your computer or network, click the “insert my IP address” button next to the scanner form to automatically pick up your IP. Then choose either to scan popular ports or specify your own list of ports. If the result says “Host seems down”, this implies that the network device of the IP address being checked blocks the ping command. However, you are advised not to use this tool to scan servers that do not belong to you.

  • Offers port scanning, proxy checkers, and other tools

  • Simple and easy to use

  • Great for testing your own networks externally

  • Fairly barebones – not ideal for advanced troubleshooting

Conclusion

Using the above online port scanners will help you find open ports on your domain or network. Those online services are easy to use and mostly targeted at SMBs that can’t afford to pay for consultants or external services to monitor their security from outside of the network.

However, please note that if your network or domain is behind a cloud proxy such as Cloudflare or SUCURI, then it may not give you accurate information. As you can see from the reviews, the NMap tool stands out among the rest.  If you are looking to learn more about it, check out this definitive NMap guide. If the online tools don’t work for you, you may check out these locally installable port scanning tools.